Solid fuel such as coal or biomass is used as fuel in combustion equipment for power generation using a boiler. When coal is used as solid fuel, raw coal is milled by a vertical mill to generate powdered coal, and the generated powdered coal is used as fuel.
The vertical mill includes a mill table that can be driven to rotate at a lower part of a housing, plural mill rollers disposed on a top surface of the mill table so as to be rotated with the rotation of the mill table and so as to receive a mill load, and a rotary classifier disposed at an upper part of the housing. With this configuration, when raw coal is supplied on the mill table from a coal feed pipe, the fed raw coal is dispersed on the whole surface due to centrifugal force to form a coal layer, and this coal layer is pressed by each mill roller to be milled. The milled powdered coal is dried by supplied air, and powdered coal with a particle diameter equal to or lower than a predetermined diameter is classified by the rotary classifier. Thus, only powdered coal with an appropriate particle diameter is discharged to the outside.
The patent literatures described below describe a classifier for a vertical mill including a conventional rotary classifier, for example. A rotary classifier for a roller mill described in the patent literature 1 includes a rotary blade formed such that a width of the blade at the upper side is larger than a width of the blade at the lower side. A rotary classifier for a mill described in the patent literature 2 is configured such that a capturing angle of a capturing classifier blade of a rotary impeller is set, and an auxiliary blade extending in the direction reverse to the rotating direction is provided on a tip end at an outer circumference side. A classifying device described in the patent literature 3 is configured such that an upper part of a rotary fin in a rotary classifier is more greatly tilted toward the rotating direction than a lower part of the fin.